4
1 Introduction
1.2.1 Water Splitting Reaction
Sustainable hydrogen can be produced from the water by splitting the molecule
directly into its elements. The process is known as water splitting reaction. The
general reaction is.
2H 2 O
2H 2 + O 2
The splitting of H-O-H bonds in the water splitting reaction can be achieved by
variety of different methods, and each method fundamentally varies from the other
in the source of power, as energy is required to break the bonds. There are different
power sources involved in the splitting of the molecules like electrical energy, thermal
energy or electromagnetic radiation. Normally, mentioned as photolysis, thermolysis,
and electrolysis [13].
All of these processes involve the use of nanotechnology for H 2 generation.
For instance, Wang et al. achieved photochemical splitting of water with the help
of quantum dots. In this investigation, a hybrid structure of carbon quantum dots
attached to the single-layer C 3 N was studied. The first-principle calculations have
depicted that the hybrid is capable of gathering visible and infrared light. These
hybrid structures were also able to prevent the mixing of hydrogen and oxygen after
their liberation from water spitting. This was due to the fact that the hybrid has sites
where redox reaction can occur, and this ensured fast delivery of the photogenerated
holes and electrons to the outer C 3 N monolayer and inner quantum dots of carbon.
The electrostatic forces of attraction forced the protons to penetrate through the
monolayer and enter the quantum dots to liberate hydrogen during electrolysis. As
no oxygen or hydrogen entered the hybrid, the mixing of the gases was prevented.
These metal-free quantum dots-assisted hybrids are appealing candidate for solar
energy-driven water splitting reactions with minimum or no mixing of the gases
[14].
Similarly, in another study, nanosheets of Ni and rGO were prepared and used for
photothermal splitting of water. The hydrogen and oxygen liberation from the water
were studied simultaneously by the use of Ni/rGO nanosheets [15]. Nanoparticles
of cobalt and nickle alloy have also been reported to possess promising electrocatalytic activity for water splitting reaction. Zhang et al. have reported metal and gas
co-doped nanosheets of carbon impregnated with iron-doped Co/Ni alloy. Fe and N
have been used for the modification of carbon nanosheets which were later doped with
the alloy nanoparticles (FeCoNi@FeNC) in order to achieve better electrocatalytic
activity. The obtained material worked as bifunctional catalyst (both for hydrogen
and oxygen evolution) in water splitting reaction. The advanced catalytic activity is
inherently linked with the existence of Fe in both nanoparticles and nanosheets, as
they promote the coordination influence between the nanosheets and nanoparticles.
FeCoNi@FeNC is used as both cathode and anode catalyst in water splitting electrolyzer, where it attained the current density of 12 mA cm
−2 at 1.63 V for 12 h
[16].
1 Introduction
1.2.1 Water Splitting Reaction
Sustainable hydrogen can be produced from the water by splitting the molecule
directly into its elements. The process is known as water splitting reaction. The
general reaction is.
2H 2 O
2H 2 + O 2
The splitting of H-O-H bonds in the water splitting reaction can be achieved by
variety of different methods, and each method fundamentally varies from the other
in the source of power, as energy is required to break the bonds. There are different
power sources involved in the splitting of the molecules like electrical energy, thermal
energy or electromagnetic radiation. Normally, mentioned as photolysis, thermolysis,
and electrolysis [13].
All of these processes involve the use of nanotechnology for H 2 generation.
For instance, Wang et al. achieved photochemical splitting of water with the help
of quantum dots. In this investigation, a hybrid structure of carbon quantum dots
attached to the single-layer C 3 N was studied. The first-principle calculations have
depicted that the hybrid is capable of gathering visible and infrared light. These
hybrid structures were also able to prevent the mixing of hydrogen and oxygen after
their liberation from water spitting. This was due to the fact that the hybrid has sites
where redox reaction can occur, and this ensured fast delivery of the photogenerated
holes and electrons to the outer C 3 N monolayer and inner quantum dots of carbon.
The electrostatic forces of attraction forced the protons to penetrate through the
monolayer and enter the quantum dots to liberate hydrogen during electrolysis. As
no oxygen or hydrogen entered the hybrid, the mixing of the gases was prevented.
These metal-free quantum dots-assisted hybrids are appealing candidate for solar
energy-driven water splitting reactions with minimum or no mixing of the gases
[14].
Similarly, in another study, nanosheets of Ni and rGO were prepared and used for
photothermal splitting of water. The hydrogen and oxygen liberation from the water
were studied simultaneously by the use of Ni/rGO nanosheets [15]. Nanoparticles
of cobalt and nickle alloy have also been reported to possess promising electrocatalytic activity for water splitting reaction. Zhang et al. have reported metal and gas
co-doped nanosheets of carbon impregnated with iron-doped Co/Ni alloy. Fe and N
have been used for the modification of carbon nanosheets which were later doped with
the alloy nanoparticles (FeCoNi@FeNC) in order to achieve better electrocatalytic
activity. The obtained material worked as bifunctional catalyst (both for hydrogen
and oxygen evolution) in water splitting reaction. The advanced catalytic activity is
inherently linked with the existence of Fe in both nanoparticles and nanosheets, as
they promote the coordination influence between the nanosheets and nanoparticles.
FeCoNi@FeNC is used as both cathode and anode catalyst in water splitting electrolyzer, where it attained the current density of 12 mA cm
−2 at 1.63 V for 12 h
[16].